1. Field of the Invention
The invention relates to an optical element for use as a viewing window which produces, together with the observer's slightly accommodating eyes, a considerable magnification of the seen far objects and a large field of vision.
2. Description of Related Art
There are telescopes generally known equipped with a tube containing the arrangement of lenses and, therefore, are unable to produce a wide field of vision. Arrangements like these are of no use as a transparent viewing window in vehicles, astronaut's helmets, etc.
There are also known telescope spectacles for far vision, the magnifying power of which are small, but which can nevertheless be worn by the user without further manipulation. An attempt to increase the magnifying power would inevitably lead to a reduction of the field of vision and to an unhandiness of such spectacles.
U.S. Pat. No. 3,611,970 discloses that a transparent viewing window for submarines is known, which correlates to the subject invention. However, even with an optimum approximation of the observer's eyes to the inner surface, this generally known transparent viewing window cannot produce an efficient magnification since the thickness of the transparent viewing window, with respect to the inner and outer radii, is not big enough. The theoretically possible magnification of this transparent viewing window has not been explained; rather it is explained that the thickness of the transparent material can be reduced by the spherical form of the observation dome at a constant resistance to pressure.